1. Field of the Invention
The present invention relates to a lens barrel and an optical apparatus allowing detection of a reference position of movable lens units.
2. Description of the Related Art
Conventionally, a lens barrel of a type in which a zoom lens unit and a focus lens unit in the lens barrel are driven by a drive unit such as a stepping motor has been known as a still camera lens barrel or a video camera lens barrel.
Generally speaking, when driving a movable lens unit by a stepping motor or the like, an open-loop control system is often adopted as the control system for the driving and positioning of the lens unit. The open-loop control system has advantages in that it is not necessary to provide a detector for detecting the position of the movable lens unit at each moment and in that the construction of the control system can be configured simpler and smaller than that of a closed-loop type control system.
However, when performing positioning control on a movable lens unit by an open-loop control system using a stepping motor, it is necessary to reset the movable lens unit to a reference position prior to starting of the positioning control in order to match the drive start position with the drive start position for the movable lens unit. Thus, it is necessary to provide for each movable lens unit a reference position detector for detecting whether or not each of the movable lens units has been set at a reset position, which is the reference position. Further, for conducting highly accurate detection of the reference position, it is ideal to arrange a light blocking portion, which is to be inserted into an opening portion of the reference position detector described below, in the periphery of a sleeve provided in a lens barrel relatively free from play.
In order to achieve a downsizing of the lens barrel, Japanese Patent Application Laid-Open No. 2002-341226 proposes a lens barrel in which, a single reference position detector detects the respective reference positions of the zoom lens unit and the focus lens unit.
In the lens barrel as disclosed in Japanese Patent Application Laid-Open No. 2002-341226, in which multiple movable lens units share a guide bar, the moving amount of the movable lens units in the optical axis direction may be large, that is, the zoom ratio may be large. In this case, it is necessary to secure a region where the movable lens units do not interfere with each other and a sleeve length required from the mechanical viewpoint for inserting the guide bar.
However, arranging the light blocking portion and the reference position detector in the periphery of the sleeve of each movable lens unit results in a rather large total length of the lens barrel, thus hindering a downsizing of the lens barrel as a whole. On the other hand, when, the reference position detector and the light blocking portion are arranged at positions away from the sleeve in order to avoid an increase in the size of the lens barrel, the positional deviation of the light blocking portion with respect to sleeve play increases, resulting in a deterioration in the precision with which the reference position detection for the movable lens units is effected.